1. The Field of the Invention
The present invention relates to mold presses. More particularly, the present invention relates to mold systems whereby corresponding mold halves are reliably maintained in a desired X-Y orientation during the molding of articles, particularly starch-bound articles.
2. The Relevant Technology
There exists a large interest in the development of articles of manufacture that are more environmentally friendly than materials such as paper, paperboard, thermoplastics, polystyrene, glass, wood, and even metals. Environmentally friendly materials of recent interest include starch-based compositions that are foamed or expanded. Such compositions are beginning to make inroads into industries such as paper, plastic, polystyrene, etc, particularly in the field of disposable containers and other packaging materials.
The last several decades has seen the proliferation of disposable articles throughout industrialized nations. The convenience of single-use articles, the need for single-use sterile articles, and the need for disposable light weight and insulative materials have caused the increased use of polystyrene as a preferred container material. Polystyrene is now being manufactured and fabricated into single-use articles, and thereafter abandoned to the environment on a significant scale. Polystyrene has the qualities of sturdiness, light weight, thermal insulation, and containment of liquids among others. Unfortunately, polystyrene is entirely non biodegradable and, although it may be substantially inert to the environment, it along with other materials such as paper, wood, and metals constitute a significant fraction of municipal landfills. Additionally, polystyrene, if incinerated, can release significantly harmful toxins into the environment. In addition to being non biodegradable, polystyrene represents the consumption of the non-renewable resource of petroleum. Additionally, time between planting a tree and harvesting can amount to several years or decades.
A substitute for polystyrene foam has been found in a foamed cellular matrix made from starch that may contain fibers and fillers. One application of containers made of a starch-bound cellular matrix was seen at the Lillihammer Winter Olympic Games where biodegradable containers made by Biopac Corporation were introduced to the public. This technology is now assigned to E. Khashoggi Industries, LLC, of Santa Barbara, Calif. One drawback to these containers was that processing and materials costs were made too high for such containers to be uneconomical viable.
Researchers at EKI have developed improved compositions for manufacturing starch-bound containers that are far less expensive than those made by Biopac. Displacement of a portion of the starch with inexpensive inorganic mineral fillers together with fibers for reinforcement have greatly reduced both materials, as well as production, costs. The result is that such articles are less expensive and more economical to produce. In addition, such articles have far better strength and other mechanical properties, which allows for the manufacture and use of articles that have substantially smaller wall thicknesses.
Another drawback to the molding process as developed by Biopac was that the molding equipment consisted of modified baking molds used to manufacture food items such as waffles, cookies, edible containers and the like. Whereas such molding systems were adequate for molding relatively thick-walled food items and containers, such as those made by Biopac, such systems have proven to be problematic when used in the manufacture of articles having smaller wall thicknesses and stricter product tolerances. An exemplary mold apparatus known in the art for manufacturing bowls is illustrated in FIG. 1.
As seen in FIG. 1, a conventional mold apparatus includes paired male and female molds joined together by a hinge mechanism. The hinge allows the male mold half to be raised up relative to the female mold in order to allow the insertion of mold material therein. Thereafter, the male mold is lowered into the female mold to yield a mated male-female mold pair having a mold cavity defined therebetween. However, hinged male and female mold pairs are prone to excessive variations in mold cavity dimensions such that maintaining a consistent mold cavity throughout an iterative molding process has proven to be quite difficult.
One problem involves the hinge. In order to provide the function of allowing the male mold to open and close relative to the female mold the hinge necessarily allows some degree of motion between the two mold halves. The problem arises where there is significant lateral movement. Even slight deviations from the ideal mating arrangement can yield an uneven mold cavity. For example, where the desired wall thickness of a given article is 2 mm, movement of the male mold by an amount of even 0.5 mm can yield an actual mold cavity having a thickness of 2.5 mm on one side and only 1.5 mm on the other. Such uneven mating not only yields a product that is substantially deformed due to the uneven wall thickness, it may also prevent proper formation of the article in the first instance.
The molding of starch-based articles having a foamed cellular matrix involves rapid expansion of the mold material as a result of formation of internal water vapor as well as removal of the water by evaporation to yield a solidified product. Because the rate of heat transfer is relatively constant between the mold and the mold material, deviations in wall thickness can greatly affect the rate at which a particular portion of the article solidifies or cures. More specifically, areas where the mold cavity is thicker than intended can yield an area of under cured material such that portion of the article upon demolding may be too soft or inadequately formed. On the other hand, overheating the article such as by leaving the article within the mold for longer than is optimal can scorch or burn the article. Thus, areas where the mold cavity is too thin compared to what is optimal may cause burning or scorching of that portion of the molded article. In view of this, the importance of properly mating the female and male molds to yield a substantially uniform mold cavity becomes readily apparent.
In addition to unwanted lateral movement between the male and female mold halves due to the hinge mechanism, which is only exacerbated as the hinge undergoes wear and tear, the mold halves can become misaligned due to fluctuations in mold temperature. It is well known that metals such as aluminum or steel used in many mold systems undergo significant expansion or contraction in response to fluctuations in temperature. Thus, heating the hinged mold apparatus depicted in FIG. 1 can cause mold misalignment due to uneven thermal expansion of the molds, particularly where the molds have varying thickness. Of course it is possible to make adjustments to the molds in order to offset the effects of thermal expansion. However, such adjustments are only feasible while the mold apparatus are not in use and the molds are sufficiently cool so as to avoid injury. Thus, such adjustments are often difficult to make and can cause significant downtime and cost in the overall manufacturing process.
It would therefore be an improvement in the art to provide mold apparatus and systems for maintaining accurate X-Y orientation between the mold halves and which overcame other problems associated with prior art mold apparatus.
It would also be an improvement in the art to provide mold apparatus and systems for molding starch-bound compositions that maintained a sufficient dimension variation tolerance and which avoided the problems associated with molding starch-bound articles having disparate wall thicknesses.
It would be a great improvement in the art to provide mold apparatus and systems that could repetitively and reliably form foamed starch-bound articles while avoiding both under curing and over curing of the starch-based compositions used to manufacture such articles.
It would also be a significant improvement in the art to provide mold apparatus and systems that consistently defined a desired mold cavity and which resisted dimensional fluctuations due to temperature variations through which the mold apparatus must cycle during the molding process.
Another improvement in the art would be to provide mold apparatus and systems that significantly eliminated the necessity of making individual mold cavity adjustments on a regular basis.
Such apparatus and methods for maintaining a desired mold cavity are disclosed and claimed herein.
The present invention encompasses apparatus and systems for molding articles of manufacture. Such apparatus and systems are configured so as to more accurately and precisely maintain proper alignment between an array of corresponding male and female mold halves, thereby better maintaining the dimensional integrity of the mold cavities defined by the male and female mold halves. This results in the ability to more consistently mold articles of manufacture having closely controlled dimensional tolerances. The inventive apparatus and systems are particularly well-suited for the manufacture of molded articles from aqueous compositions which solidify as a substantial portion of the water is driven off by evaporation. Examples of aqueous compositions suitable for use in combination with the inventive apparatus and systems are aqueous starch-based compositions.
In general, the mold apparatus used in the inventive systems comprises a plurality of male and female molds mounted in a pair of two-dimensional planar arrays, with the female molds occupying a first planar array and the male molds occupying a second planar array. The male and female molds within their respective planar arrays are configured and oriented so that the male and female molds will mate to form an array of desired mold cavities. By means of the first and second planar arrays of adjacent molds, the possible degrees of freedom of the various molds are greatly reduced.
The inventive mold press apparatus do not utilize hinged male and female mold pairs. Elimination of the hinges greatly reduces mold misalignment inherent in hinged mold pairs. In addition, the molds within the mold arrays preferably make abutting contact with each other, thereby reducing the tendency of individual molds to slip out of adjustment. The array or grid of molds causes the individual molds to essentially interlock so as to create a plurality of fixed mold halves with little or no freedom to move or slip.
In addition to, or instead of, the molds making abutting contact, the corresponding male and female molds can have interlocking features which ensure proper mating and a reproducible mold cavity. This allows the molds to be self-adjusting.
The foregoing features of the inventive mold apparatus ensure more uniform and reproducible wall thicknesses of the molded articles. More particularly, minimizing fluctuations in the size and configuration of the mold cavities ensures predictable and uniform wall thicknesses during numerous iterations of the molding process. This, in turn, helps to ensure the proper baking time in order to yield molded articles in which the article as a whole has been adequately, but not overly, baked or heated within the mold. Maintaining proper wall thicknesses allows the technician to select a baking time and temperature that will ensure adequate harding of the starting composition while avoiding charring or burning of the starch binder and other heat-sensitive components.
In a preferred embodiment of the present invention the male and female mold arrays are arranged in a parallel-planar orientation. In this embodiment, the arrays of molds male and female comprise rectilinear arrayed structures that are fastened or aligned together to make a substantially larger composite rectilinear structure. Each of the structures may comprise a series of one-, two- or multi-compartment molds for manufacturing one-piece, hinged two-piece, or multi-pieced articles. Maintaining proper X-Y alignment between the male and female molds in especially important when attempting to mold two-piece and multi-piece articles of manufacture.
Examples of one-piece articles include plates, bowls, trays and boxes. An example of a hinged two-piece article is a xe2x80x9cclam-shellxe2x80x9d sandwich or burger container. An example of the hinged three-piece article is duel hinged claim-shell container. An example of a multiz piece article is a box or other container with a lid or top.
In a preferred embodiment, the mold apparatus will be adapted for use in molding articles from aqueous starch-based compositions. Examples of starch-based compositions and methods for molding such compositions into useful starch-bound articles of manufacture are set forth more fully in U.S. Pat. No. 5,618,341; 5,660,900; 5,662,731; 5,679,145; 5,683,772; 5,705,203; 5,709,827; 5,776,388; 5,783,126; 5,843,544; and 5,868,824. The foregoing patents are presently assigned to E. Khashoggi Industries, LLC, located in Santa Barbara, Calif. For purposes of disclosure, the foregoing patents are incorporated herein by specific reference.
Starch-based compositions typically including water, ungelatinized and/or pregelatinized starch, fibers, an inorganic filler and optional components such as a mold release agent. During the molding process, the heated molds preferably cause a sudden increase in the temperature of the aqueous starch-based compositions. This causes the initially ungelatinized starch granules to become gelatinized while also causing a buildup of pressure within the mold cavity due to the formation of water vapor.
In a preferred embodiment, the mold apparatus according to the present invention will include venting means for allowing a controlled amount of water vapor to escape from the individual molds during the heated molding process. Allowing only a controlled rate of water vapor release provides for a desired level of internal pressure buildup within the mold cavity, which assists in causing or allowing the starch-based composition to expand and fill the mold cavity. The venting means will typically include one or more vent holes and/or a venting ring at or near the interface of the male and female molds. The vent holes and/or venting ring should be oriented so as to ensure that the entire mold cavity is filled during the molding process. Otherwise, localized buildups in pressure could cause certain sectors of the mold cavity to resist being filled by the expanding mold composition.
It is therefore an object of the invention to provide mold apparatus and systems for maintaining accurate X-Y orientation between the mold halves and which overcome other problems associated with prior art mold designs.
It is also an object and feature of the invention to provide mold apparatus and systems for molding starch-bound compositions that maintain a sufficient dimension variation tolerance and which avoid the problems associated with molding starch-bound articles having disparate wall thicknesses.
It is a further object to provide mold apparatus and systems that can repetitively and reliably form foamed starch-bound articles while avoiding both under curing and over curing of the starch-based compositions used to manufacture such articles.
It is another object to provide mold apparatus and systems that consistently define a desired mold cavity and which resist dimensional fluctuations due to temperature variations through which the mold apparatus must cycle during the molding process.
It is yet another object and feature of the invention to provide mold apparatus and systems that significantly eliminate the necessity of making individual mold cavity adjustments on a regular basis.
These and other objects and features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.